i6s \ PRACTICAL ORGANIC CHEMISTRY
the copper powder is gradually added. It is prepared by dis-
solving 100 grams crystallised copper sulphate in 300 c.c. water
and dusting in through a fine muslin bag 25 grams zinc dust with
constant stirring. It is left until the blue colour of the copper
salt has nearly disappeared. The precipitated powder is washed
' •"; by decantation two or three times with cold water and then with
very dilute hydrochloric acid to remove metallic zinc and
finally filtered and washed at the pump. The pasty mass is not
allowed to dry, but is added at once in small quantities to the
diazonium solution with constant stirring. After the evolution
of nitrogen has ceased the bromotoluene is distilled in steam
and purified as described above. See Appendix^ p. 284,
Griess, Annalen, 1866, 137, 76.
25 grms. /-toluidine.
50 „ (27 c.c.) cone, sulphuric acid (in 250 c.c. water).
20 „ sodium nitrite (in 40 c.c. water).
60 „ potassium iodide (in 100 c.c. water).
Mix the dilute sulphuric acid and /-toluidine in a larg-e
beaker (f litre) and cool to o° in a freezing mixture. Stir,
whilst cooling, to produce small crystals of the sulphate. Axlcl
the solution of sodium nitrite slowly, and if the temperature
rises above 10°, add a few lumps of ice. When three-quarters
of the nitrite solution has been added, test occasionally with
potassium iodide-starch paper until a blue or brown stain is
produced. Now add the solution of potassium iodide gradually,
and, after well stirring, leave the mixture at the ordinary temper-
ature for an hour, and then warm cautiously on the water-bath
until effervescence ceases. The liquid is dark coloured, and a
black oil settles to the bottom of the vessel, which when cold
solidifies. The oil consists of iodotoluene, and the dark colour of
the solution is due to free iodine, which may be removed by the
addition of a gram or two of sodium- bisulphite. The mixture
is now distilled in steam, using a beaker as receiver. Care must
, | be taken to prevent the condenser tube becoming blocked by the
| iodotoluene, which is solid at the ordinary temperature. This is